503 Service Unavailable

I am really tired of 503 errors. I have setup a new apache server and transferring some of my websites to apache. I have tried all versions, including 4.1.0RC1 and compiled php several times (5.2.8, 5.2.9, 5.2.10) but no luck. What is the exact cause of this problem and how can I fix? I have two servers with this problem and I am in a very big trouble...
Thanks in advance...

I am sorry but my experiences are same about 503 errors. It is rondom, sometimes people get 503 error, somtimes blank pages. Is there a link to download older versions like 4.0.4? There was no problem with this version.

BTW I really want to undersand the reason. For example what causes to "Max retries has been reached, 503!". May be there can is a configuration issue. I really need urgent help...

Yes I have tried that but iy gives 404. I think older versions are deleted from download repo. I have completely deleted whole lsws directory and made a fresh install but no luck. I have randomized 503 pages...